1. Field of the Invention
The present invention relates to a navigation device and a navigation system which obtain information such as map data or the like via communication.
2. Description of the Related Art
When a navigation device which obtains information such as map data and the like through communication with a sever device performs communication via a communication device fitted in the navigation device which is mounted in a vehicle and the like, or a communication device carried by a user (for example, a mobile terminal, such as a cell phone or the like), the following problems will occur due to a communication condition such as the type and functions or the like of the communication device, and a communication state relevant to areas and time slots or the like. Specifically, take a cell phone for an example. The performance on communication speed of a cell phone differs according to the development on the communication method and model thereof. Therefore, in the case where the navigation device sets a communication parameter such as a time-out value, a retry number of times or the like to fit a cell phone of an old model (with low communication speed performance), it is possible to support plural models of cell phones, however, this will cause a cell phone with high communication speed performance waiting for a longer time, which is inconvenient. On the other hand, in the case where the navigation device sets the communication parameter to fit a cell phone with high communication speed performance, it is impossible to support plural models of cell phones. Therefore, it is desirable to modify the communication parameter so as to fit a cell phone. Further, a cell phone of a newer model may be on sale after the shipment of the navigation device, thereby, it is conceivable that the communication parameter pre-installed in the navigation device may not work appropriately on the cell phone of a newer model.
Moreover, the coverage (available communication area) of a cell phone differs according to each carrier (communication service provided by communication service providing company). Further, the magnitude of electromagnetic waves varies at different communication locations. Therefore, in the case where a user is in an unavailable communication area, inappropriate configuration of the communication parameter will cause the user waiting for a longer time, or consume the battery of the cell phone due to frequent connection retry. In addition, since the coverage of a cell phone varies according to the addition or development of implants, it is desirable to modify the communication parameter to fit the coverage variation of the cell phone. However, it is difficult for the user to appropriately modify the communication parameter personally so as to fit a particular coverage condition.
Further, it is necessary to set a time-out value of the communication parameter longer in a time slot when the communication is congested (for example, early in the evening) than the other time slots. However, as the configuration of the time-out value depends on the communication congestion, it is difficult for a user to set appropriately the communication parameter according to the communication congestion at a particular time slot.
Regarding the above cases, there has been disclosed a device which modifies a configuration of the communication parameter according to the communication condition in Japanese Patent Laid-open No. H7-141273. The communication performance processing device, as a prior art, carries out a communication control process by sequentially configuring different communication control parameters, obtains determination values by monitoring the communication under each of the communication control parameters, and sets an optimal communication control parameter by mutually comparing the obtained determination values.
However, according to the communication performance processing device, it is necessary to perform repeatedly the communication control process by sequentially varying the communication control parameters in a predefined range which is set on the basis of predefined initial values and to compare mutually the determination values so as to determine the optimal communication control parameters. Therefore, it is disadvantageous since it costs longer time to determine the optimal communication control parameters.